Waste pipes - Gradient - length and connection to Soil Stack

[HomerHart]

Right here goes:

I am at the planning stage of totally refitting my bathroom.

I am by no means a 'Plumber' but have done some plumbing DIY stuff before.

I am moving the bath to the other side of the room, moving the sink to another wall, installing a new shower cubicle and am intending to have all the waste pipes under the floor boards (Yeah, I know that I am making life difficult and that if one leaks it will be difficult to get to and so on...)

The main questions I have are around the pipe gradient, siphonage, air blocks and all that stuff - I have read up about these on the internet and just end up getting more confused and scared of doing anything.

Anyway.......

The idea is to have the bath connected to the soil stack by itself - this will be above the floor boards as it will all be hidden by the bath panel as the soil stack is at the end of the bath. Then on the opposite side about a foot lower down will be the WC inlet into the soil stack. I then have a shower and a sink to route - I was going to run the shower waste under the floor boards and the join the sink waste onto the shower waste with a swept tee and then across to the soil stack. I was going to use 40mm pipes for this as they will have to be through the floor joists and think that 50mm holes in the floor joists sounds BAD!
The next problem I have is that the Shower/Sink waste will be at a similar height to the WC waste. It could go perpendicluar to the WC connection which I understand is OK? BUT where the WC joins the stack there there is a wider section of pipe (the Boss I believe it is called) so don't think I can attach to that so was going torun the pipes horizontally (with a gradient obviously) under the floor and then when it is close to the soil stack have a 90 degree bend sending the waste pipe vertical and parallel to the soil stack and then another 90 or 45 degree bend and then connect to the soil stack lower down avoiding the 200-250mm no go zone in relation to the WC connection above. Is this okay???? I have read that there are minimum and maximum gradients for waste pipes and maximum drops etc so I just wonder if having this vertical section before the soil stack would mean that I would exceed the maximum drop/gradient and end up with siphonage problems???? I have looked into HepVo valves to get around the siphonage problem but the shower is a low profile one and requires a high flow waste and therefore I don't think a HepVo would be compatable.
I do have some drawing to explain this all a bit better but I don't know how to post them yet.

Any responses welcomed.....

 

[Softus]

...am intending to have all the waste pipes under the floor boards

Don't.

The main questions I have are around the pipe gradient, siphonage, air blocks and all that stuff - I have read up about these on the internet and just end up getting more confused and scared of doing anything.

I don't understand which part of it you're finding confusing. Do you have any specific question(s) about pipe gradients?

The idea is to have the bath connected to the soil stack by itself - this will be above the floor boards as it will all be hidden by the bath panel as the soil stack is at the end of the bath. Then on the opposite side about a foot lower down will be the WC inlet into the soil stack.

Is the soil stack outside or inside? It's hard to imagine that it could be inside if you're planning a 110mm connection one foot lower then the bath waste connection, so this is where a diagram would be invaluable.

I then have a shower and a sink to route - I was going to run the shower waste under the floor boards and the join the sink waste onto the shower waste with a swept tee and then across to the soil stack.

No problem with the swept tee, but I don't see how you're going to notch joists for 40mm pipe (which, BTW, measures about 45mm in external diameter) without risking your house falling down.

The next problem I have is that the Shower/Sink waste will be at a similar height to the WC waste.

Similar? I'm getting lost now - is it higher or lower?

...was going torun the pipes horizontally (with a gradient obviously) under the floor and then when it is close to the soil stack have a 90 degree bend sending the waste pipe vertical and parallel to the soil stack and then another 90 or 45 degree bend and then connect to the soil stack lower down avoiding the 200-250mm no go zone in relation to the WC connection above. Is this okay?

Yes - it sounds better then the other options. Except for the under-the-floor part.

I have read that there are minimum and maximum gradients for waste pipes and maximum drops etc so I just wonder if having this vertical section before the soil stack would mean that I would exceed the maximum drop/gradient and end up with siphonage problems?

Gradients are to do with horizontal pipe runs.

...the shower is a low profile one

What's a low profile shower?

I do have some drawing to explain this all a bit better but I don't know how to post them yet.

See this:
//www.diynot.com/forums/viewtopic.php?t=99672

and this:
//www.diynot.com/forums/viewtopic.php?t=91713

 

[bengasman]

Gradient is simple; at all times you need a fall of at least 2.5 degrees which equals roughly 40 mm vertical for every meter horizontal. I have come across instructions for 500mm per metre.
You can NOT drill 50 mm holes at a 4% fall in joists EVER. IF you drill holes in a joist, they have to be in the middle vertically. Always. I never need holes that big so I do not remember the max diameter but it is 1/8 or ¼ of the joist height max. There is also a very limited area where you are allowed to drill holes with respect to the span of the joist in respect to the span. If you can run the pipe along the joists, you need to subtract the o.d. plus 10 mm from the workable height between ceiling and floor to find the maximum length you can run the pipe. I.e. 7 inch joist, minus 15mm ceiling supports, minus 40mm pipe, minus 10mm leaves 110 mm. Multiply this by 25 and you are left with 2.5 in stead of in stead of 4.5 metres. And you also have to include the length of pipe needed to go through the wall. Finally, every bend needs to be rodable.

 

[Softus]

Gradient is simple; at all times you need a fall of at least 2.5 degrees which equals roughly 40 mm vertical for every meter horizontal.

Er, no it isn't.

Finally, every bend needs to be rodable.

Really? In 40mm pipe? Why?

 

[bengasman]

Gradient is simple; at all times you need a fall of at least 2.5 degrees which equals roughly 40 mm vertical for every meter horizontal.

Er, no it isn't.

Finally, every bend needs to be rodable.

Really? In 40mm pipe? Why?

I meant every length, not every bent. Reason? because building boys, sorry I mean persons, throw a wobly if you do not.

As for the 2.5 degrees, do tell me what it should be. If half possible with a pointer as to where this is specified. Personally, i do not really care as long as it works and will be approved by building control, i am happy.

 

[ChrisR]

iirc the Bldg Regs say between 9 and 90mm per metre for falls. Suggest you stick to about 1 in 40 = 25mm/metre = approx 1.5º for soil pipes.

Ensure even gradients, suport to prevent sagging.

Don't drill joists for waste pipes, on the whole.

Take em all outside before joining, wherever practical.

NB shower traps need a 50mm seal, the 19mm ones everyone uses are illegal afaik.

 

[denso13]

http://www.marleyplumbinganddrainage.com/images/productguides/Waste & Overflow1.pdf

Minimum 20mm per m run, which is just over 1 degree (I think!!)

 

[hi-spec plumbing heating]

iirc the Bldg Regs say between 9 and 90mm per metre for falls. Suggest you stick to about 1 in 40 = 25mm/metre = approx 1.5º for soil pipes.

Ensure even gradients, suport to prevent sagging.

Don't drill joists for waste pipes, on the whole.

Take em all outside before joining, wherever practical.

NB shower traps need a 50mm seal, the 19mm ones everyone uses are illegal afaik.

looking at most of your posts on drainage, i think you seriously need to read the regs again.

19mm is not illegal. they where in older installation before the current regs. in which they still can be used on a early install as a direct replacement for a worn one.

shower traps of 50mm are not the min 38mm providing it is directed to a gully.

as for 9 / 90mm 0n a soilpipe is wrong rain water yes soil is 18 mm